1. Field of the Invention
The present invention relates to filters which are used, for example, in extra corporeal circuits for removal of particulate and gaseous matter. Particularly, embodiments of the present invention relate to a disposable arterial blood filter for use in extra corporeal blood flow circuits, such as in a bypass circuit, for filtering out solid or gaseous emboli.
2. Description of Related Art
Disposable arterial filters have been used for the treatment and filtration of blood for various applications such as cardiopulmonary bypass techniques, blood transfusions, dialysis treatments, etc. The arterial filter is provided to trap and remove gaseous and particulate matter from oxygenated blood. Typically, the arterial filter is one of the components in an extracorporeal blood flow circuit in which blood flows from a patient's body, through a cardiotomy reservoir, an oxygenator, and finally into the arterial filter before it is returned to the patient. Thus, the arterial filter may be the last component of the extracorporeal blood flow circuit through which blood traverses before it returns to the patient.
Certain conventional blood filters include a hollow tubular housing containing a concentric cylindrical filter element and a perforated tubular core disposed inside the cylindrical filter element. U.S. Pat. No. Re. 32,711 to Dickens et al. discloses such an arterial filter design. The perforated core is provided to support, or brace, the filter material within the tubular housing and is thus designed to reduce the possibility of collapse at high flow rates.
This type of conventional structure typically utilizes a pleated filter element contained within a tubular housing unit having a dome-shaped cover. A perforated plastic core is concentrically disposed in the center of the cylindrical filter material to support, or hold up, the filter element within the housing. A conical cap forming an upwardly directed peak separates the end of the cylindrical filter material from a generally flat housing cover. A gas vent is centrally disposed at the apex of the dome-shaped housing cover. The conical cap causes inlet blood to swirl and create a vortex between the conical cap and the housing cover. This vortex action purportedly drives gaseous matter toward the center of the housing cover to escape through the gas vent located at the center of the cover.
In such designs, however, because the gas vent is located at the center of the housing cover (displaced from the outer periphery portion of the cover), and because the filter cap inside the housing forms a peak at its center, there is limited visibility of the filtration process from inlet to outlet. Thus, confirmation of the filter properly receiving and passing blood and of proper debubbling and uniform filtration of the liquid may be difficult if not impossible.
In addition, because such conventional blood filters typically employ a coarse outer support screen, such as netting or other large-pored materials, bubbles in the liquid often become undesirably entrapped within the gaps in the outer filter material. Consequently, such conventional blood filters require rigorous and prolonged agitation of the fluid inside the filter housing to dislodge any bubbles trapped during both the priming process and actual filtration. As a result, to minimize damage to the filter media during the prolonged agitation, the perforated core is provided to support the filter element as it is impacted by the agitated fluid flowing within the housing.
Moreover, although such conventional arterial filters provide a finer inner filter layer adjacent the coarse, large-pored external filter material, the desired orderly venting of gas often cannot be attained due to the presence of gaseous matter which may already have collected in the coarse outer filter layer. As a consequence, further agitation may be necessary to loosen and prevent any gaseous emboli from passing through the filter layers.